I have annotated photos to go with this how-to. If someone would please suggest how to link or otherwise include, I will do so.

Oscar is now successfully desaled. I was nervous about this after reading so many stories of various machines breaking or malfunctioning after descaling. But with smelly steam and a decent amount of debris emptied from a simple drain, a good boiler descale was in order.

Thanks to the great ideas here and on other sites, it looks to have gone just fine. The tip to disconnect the heater element and fill level switch worked brilliantly to overfill the boiler. After draining the boiler, four pump runs of about 30 seconds each, with a bit of rest between, filled the boiler to the top and eventually caused water to flow from the steam wand. I let the acid work for about 30 minutes before draining. I did three fills with citric acid based on the amount of junk coming out, each time getting a bit weaker, followed by three (or maybe four) plain water flushes.

Here is the procedure as I recall it – it was over a week ago now and I’m using memory and photos to recall. Before fiddling with any electrical connections or flipping the machine over, I always unplugged the power cord.

Remove the top cover. Easy - six screws and wiggle the top housing loose. Unplug the power cord and disconnect the fill level sensor on top of the boiler.

Remove the reservoir tank and drip tray. You can do this before or after removing the top housing.

Put down a heavy bath towel or something similar and carefully turn Oscar upside down. It’s a heavy machine so be sure to grab strong parts while lifting and turning. The steel frame is best but a frame grab point may not always be handy.

Disconnect the boiler heater. I couldn’t do this with the bottom cover in place. Remove the four screws from the plastic body bottom, not the ones in the metal plate. The bottom cover can then be flipped over toward the drip tray. Here is a link that includes a video for how it works (thanks coffenoobie!): http://www.elektros.it/en/tips-and-tricks.html

Remember to disconnect the boiler heater.

Flip the machine onto its left side. Here is where the padding from the bath towel or soft throw rug helps in keeping the plastic case exterior free from scratches. Slide Oscar over to the edge of a sink, table, or other work surface to position the drain pipe into a large bowl. With no other diverter or flume, water will drain inside the steel frame, between the frame and the work surface edge. If working over a sink, you could just drain straight to the sink drain, but I wanted to see what came out with the water to gage how many fills and flushes were needed.

Remove the drain nut and plug under it and allow water to flow into the bowl. Opening the steam valve should allow air to enter the boiler from there and make draining faster. However, during my first couple of drain runs, no air would enter through the wand resulting in a slow drain- glug, drain- glug routine. When the draining slowed, I wiggled and rocked the machine to slosh the remaining water in the boiler around and coax it out of the drain. It was then that good batch of debris came out that had not found the little drain hole earlier.

After the first citric acid soak and drain, here is what came out. Markarian, you were right about the Mutant Ninja Turtle sludge; it was green and heavy with debris. A good amount of the crud looked like white flakes in the water, making plausible Coffeenoobie’s notion that milk might have been sucked back into the boiler through the steam wand, causing the nasty smell.

Once completely drained, reinstall the drain plug and nut. I tightened by hand because there would be no pressure in the boiler and the nut was coming off again soon anyway.

Flip the bottom cover back into position and secure with a couple screws just to keep it in place while turning the machine back over. These screws will also be coming out soon and I saw no need for all four screws. Just be careful while handing the frame and case.

Turn Oscar back upright, insert the reservoir, and plug it in. There’s no need to put the top cover back on. Refill the reservoir with citric acid solution if you want to do another soak, or clean water if you’re ready to flush and rinse.

Now, the process becomes repetitive. Repeat the acid fill and soak for as many times as you think are necessary based on the debris draining. I did three acid soaks of about 30 minutes each for the sake of limited time. Not only did less gunk come out, the water became progressively less green with each cycle.

By the third acid drain, air was entering through the steam wand and water flowed out of the drain pipe much more freely, eventually becoming a steady flow. Apparently, the steam pipe or valve was partially plugged enough to prevent the low pressure vacuum from flowing in.

After the last acid drain, rinse the reservoir with clean water to remove any remaining acid, refill with clean water. Repeat the fill-drain process to flush any acid from the system. After the boiler fills completely, let water flow from the wand for a bit to make sure any debris gets flushed. In my case, I had some crud coming out of the wand. More crud came from the boiler, too, especially when the water got the bottom and I rocked and wiggled the machine to get the last splashes out.

Even on the last clean water flush, I coaxed debris out at the end of the draining process. I’m sure there is still some crud in there, but this all took several hours and it was getting pretty late on a “school” night. I’d guess that enough rock, crud, scale, floaty-flakes, and other nastiness came out to measure a solid mass between a quarter and half cup. Whatever is left must be a small fraction of that amount. I’ll just have to look forward to another round in a few months.

Here are a few miscellaneous tips:

This process involves a lot of flipping the machine upside down and onto its side. Use a thick bath towel or soft rug to absorb the inevitable ounces of water that will spill from the reservoir fill valve. The padding will also protect and plastic case finish. I caused a few scratches on the side before realizing it was happening.

Don’t forget to disconnect the boiler heater before starting. Otherwise, it can quickly burn out while energized and exposed to air instead of water. Disconnecting the boiler heater requires opening the bottom cover.

I found a couple suggestions for checking when the rinse cycles are adequate. 1) Dip your finger into the drained water and if it tastes sour or of citrus, keep rinsing. 2) Add some baking soda to the drained water and if it fizzes, keep rinsing. I did the taste test which seemed to work fine.

Before reconnecting the heater, remember to have the fill level sensor reconnected and tank filled to the normal level. Otherwise, you risk a nonfunctioning machine needing a new boiler heating element.

After all was done and refilled, I let Oscar sit overnight to allow any stray water that may have contacted electrical parts to dry as much as possible. There was only one real spill of an ounce or so while filling the reservoir that may have made it the bottom cover hiding the pump and Gicar. Being late, I had no intention of making a coffee and there was no reason to risk frying something by energizing the machine more than necessary.

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